The Hispanic Community Health Study (HCHS) is a prospective cohort study to identify prevalence and determinants of many diseases and disorders in Hispanic populations residing in the US, with major representation of four ethnic origins (Central/South American, Cuban, Mexican, and Puerto Rican). The subjects will come from population groups originating from multiple geographic areas and founder populations, and with residence in the US for varying lengths of time, ranging from many generations to less than a year. Funding is provided by NHLBI, NIDDK, NINDS, NIDCR, NIDCD, NCMHD, and ODS. Each Institute or Center contributes funding for support of the core functions of the study and components of interest specified by each contributing sponsor. Procedures for each enrolled subject include measurement of blood pressure, anthropometry, physical activity, spirometry, sleep studies, ECG, dental examination, hearing examination, and cognitive status measurement. NIDCD is providing funding to support audiometry exams and questions relating to hearing loss/hearing aid use, tinnitus, noise exposure, and other factors that affect hearing thresholds. The hearing examination will include otoscopy, acoustic immittance and both air-conduction and bone-conduction pure tone audiometry. The NHLBI is the representative to the Steering Committee and conducts this role with input from each contributing sponsor. The Hispanic population is now the largest minority population in the US with a projected three-fold growth by 2050. Hispanics are influenced by factors less commonly found in other US population groups, including changes in diet, activity, community support, working conditions, and health care access, particularly as these changes are associated with immigration from different cultural settings and environments. They are experiencing increasing obesity, higher risk of diabetes, and changes in social and behavioral factors with large potential impact on many major chronic diseases. These differing cultural and genetic backgrounds can have a large potential to influence disease risk. Hispanic populations are very much understudied with respect to many diseases. Their disproportionately lower economic status results in significant disparities in health care. Compared to non-Hispanics, Mexican Americans are half as likely to have their hypertension controlled, more than twice as often report no usual health care, have a greater prevalence of reported fair or poor health, and are twice as likely to have no health insurance. Asthma appears to be a particular problem in some Hispanic subgroups, and chronic otitis media is increased among Hispanic children studied in the National Health and Nutrition Examination Survey (NHANES). Longitudinal cohort studies in Hispanic populations are needed to understand the development of risk factors and disease in these populations, and to apply the knowledge gained to prevention of disease in the entire US population.